I've done this quest a number of times as I've been living in the Orc Fort in Eastern Wastes. Both the molds and materials drop off the Orcs as well as Snow Griffons and Manticores. Boots, bracers, helmet, glove mold seems to drop as common. Sleeves seem to be uncommon and legs and tunics rare drops. As Marglar said, you don't need invis to reach him.
Here's some of my quest log:
[Sat Jun 05 10:57:17 2004] You say, 'Hail, Craftsman Charek'
[Sat Jun 05 10:57:17 2004] Craftsman Charek says, 'Many greetings, friend. You are welcome to the shore of the Othmirs, and our shelter is yours. I am Charek, tailor and smith of the Othmir. Judging from your appearance, I'd say you're another adventurer, come to the cold wastes of these lands. Hmm, perhaps you would be interested in something I've found out... its in regards to a lost way of crafting [armor].'
[Sat Jun 05 10:57:30 2004] You say, 'what armor?'
[Sat Jun 05 10:57:30 2004] Craftsman Charek nods, 'When diving for shells recently, some of our fishers came upon an ancient seachest half-buried in the sand near one of the many shipwrecks here. They pulled it out onto the shore, and it turned out, oddly enough, to contain [molds] and [materials] clearly made for the crafting of four different kinds of armor.'
[Sat Jun 05 10:57:30 2004] Craftsman Charek says, 'If you could find out where more such [molds] and [materials] can be found, I can craft armor of your preference for you - simply bring me one of the material types along with a mold, and I will make what I can out of it.'
[Sat Jun 05 10:57:48 2004] You say, 'what molds?'
[Sat Jun 05 10:57:48 2004] Craftsman Charek says, 'The molds I have located so far are rather ancient by the looks of them, and cut for the following pieces of armor... Headgear, tunics, sleeves, leggings, gloves, bracers and boots.'
[Sat Jun 05 10:57:57 2004] You say, 'what materials?'
[Sat Jun 05 10:57:58 2004] Craftsman Charek says, 'The materials I speak of are gold-tinted sheets of metal - they glow faintly, and can be used to make exceptional platemail, slightly greyish links of chainmail naturally used for the making of such chainmail armor, straps of boiled leather with dull runes inprinted onto them, for making leather armor... And finally rolls of very fine, ornately cut silk - out of which I can make quite powerful magical silk armor.'
[Sat Jun 05 11:14:12 2004] Craftsman Charek says, 'Ah! A mold and some materials, let me see what I can make out of this. Hmm.. interesting. Well, here you go, may it serve you well.'
As for rewards: (and I haven't turned in any silk)
REWARD: Masterwork Golden Platemail Boots - feet - nodop, AC9 sta +2 wis +1 int +1 svcold +2 wt6.1 War CLR Pal SK Brd
REWARD: Masterwork Golden Platemail Helmet - Head - nodop, AC11 wis +2 int +2 Mana+10 wt7 War CLR Pal SK Brd
REWARD: Masterwork Golden Platemail Bracer - Wrist - nodop, AC8 dex +2 agi +2 Mana+10 wt4 War CLR Pal SK Brd
REWARD: Masterwork Golden Platemail Gloves - Hands - nodop, AC11 hp+10 Mana+30 wt6.5 War CLR Pal SK Brd
REWARD: Masterwork Golden Platemail Chestplate - Chest - nodop, AC20 str+5 hp+25 wt18 War CLR Pal SK Brd
REWARD: Masterwork Golden Platemail Greaves - Legs - nodop, AC14 agi +3 svfire+1 svcold+1 svpsn+1 svdis+1 wt12 War CLR Pal SK Brd
REWARD: Masterwork Golden Platemail Vambraces - Arms - nodop, AC12 ch+3 svfire+4 wt8.5 War CLR Pal SK Brd
REWARD: Runewoven Leather Leggings - Legs - nodrop, AC8 str+2, wis+2, svcold+2 wt.8 Dru Mnk Bst
REWARD: Runewoven Leather Arms - Arms - nodrop, AC7 dex+2, hp+15, wt.6 Dru Mnk Bst
REWARD: Runewoven Leather Gloves - Hands - nodrop, AC4 ch+3, hp+10, wt.2 Dru Mnk Bst
REWARD: Runewoven Leather Boots - Feet - nodrop, AC4 hp+25, wt.4 Dru Mnk Bst
REWARD: Runewoven Leather Wristband - Wrist - nodrop, AC3 wis+2 mana+5 svdis+1 hp+10, wt.1 Dru Mnk Bst
REWARD: Runewoven Leather Skullcap - Head - nodrop, AC5 ch+3 agi+2 wt.2 Dru Mnk Bst
A side note, an alternative to this quest is to hunt in Nurga for Skulker's armor. My troll beastlord has been living in there and he kind of wears a mix of Skulker's and Runewoven now.